British Prime Minister Boris Johnson said on Wednesday he will take the vaccine developed by AstraZeneca after a number of European countries halted their rollout of the jab over safety fears.

Johnson dismissed questions in parliament about why several countries had suspended use of the product developed by the British-Swedish pharmaceutical company with scientists at Oxford University.

But he told lawmakers: "I finally got news and I've got to have my own jab, very shortly, I'm pleased to discover.

"It will certainly be Oxford AstraZeneca, that I will be having."

Johnson, 56, is among the next category of people being called for vaccination. The government hopes to have offered it to all adults by July.

Health Secretary Matt Hancock said that timeline remains on track, despite the National Health Service in England warning in a letter to administrators that vaccine supplies will be "significantly constrained" from March 29 for up to a month.

"Vaccine supply is always lumpy and we regularly send out technical letters to the NHS to explain the ups and downs of the supply over the future weeks," Hancock told a news conference, insisting the letter was "standard" practice.

Britain has now given more than 25 million people a first dose of a Covid vaccine -- including 11 million doses of the AstraZeneca jab -- after starting a mass inoculation programme in December last year.

It is also using a jab developed by Pfizer/BioNTech in its rollout programme but recipients do not normally get a choice of vaccines.

Johnson wrote in the Times newspaper that the AstraZeneca vaccine "is safe and works extremely well". Hancock and England's deputy chief medical officer Jonathan Van-Tam echoed that assurance at the press conference.

- Royal intervention -

European countries including France, Spain and Germany are among those who have halted using the jab pending a review by the European Medicines Agency (EMA) amid feared links to blood clots and brain haemorrhages.

Queen Elizabeth II's oldest son and heir, Prince Charles, on Wednesday criticised opposition to coronavirus vaccines.

"Who would have thought, for instance, that in the 21st century that there would be a significant lobby opposing vaccination, given its track record in eradicating so many terrible diseases," he said in an article in the Future Healthcare Journal.

Charles, who has been vocal in advocating the rollout of the vaccine among more reluctant minority communities in Britain, added that the jab had the "potential to protect and liberate some of the most vulnerable in our society from coronavirus".

The 72-year-old Prince of Wales tested positive for coronavirus last year and suffered mild symptoms. He had his first dose of a vaccine in February.

His wife, Camilla, 73, confirmed on Tuesday she had been given the AstraZeneca shot.

"You take what you are given," she said as the couple visited a vaccination centre at a north London mosque, adding that she had suffered no ill-effects.

- 'No evidence' -

Professor Jeremy Brown, from the government's Joint Committee on Vaccination and Immunisation (JCVI), said suspension of the AstraZeneca jab was "not logical".

"There is the concern that what's happening in Europe might make people in the UK less confident in the AstraZeneca vaccine," he told broadcaster ITV.

The EMA, the World Health Organization and Britain's Medicines and Healthcare products Regulatory Agency have all backed the AstraZeneca jab.

France and Italy have said they will "promptly restart" giving the jab if the EMA review allows it.

As Britain has surged ahead with its vaccination programme, European countries have been accused of playing politics to distract from their sluggish inoculation rollouts.

European leaders were angered in January after AstraZeneca announced it was unable to deliver the agreed numbers of jabs to the bloc.